Research On The Design And Grinding Method For Variable Ratio Rack Of Mechanical Variable Ratio Steering Gear

Mechanical variable ratio(all known as variable transmission ratio,this paper is referred to as "variable ratio")steering gear can relieve the contradiction between the steering portability and the sensitivity.It realizes the variable ratio function through the transmission of the variable ratio rack and the involute gear.Variable ratio rack tooth surface is a complex surface,consisting of working tooth surface and blending surface.In order to design the variable ratio rack more efficiently and accurately,this paper proposes a digital design analytical method of variable ratio rack of mechanical variable ratio steering gear based on the meshing theory.According to the tooth surface’s characteristics of variable ratio rack,a grinding method based on two-parameter envelope is proposed to provide theoretical basis for finishing of variable ratio rack.The main research work of this paper includes:(1)From the perspective of design principles,the existing design method of variable ratio rack is analyzed and compared,and on this basis,a digital design analytical method of variable ratio rack of mechanical variable ratio steering gear is proposed.Based on the meshing theory,the space coordinate system and coordinate transformation matrix are established,the working tooth surface equation,blending surface equation and meshing equation of the rack are derived,and then a solution algorithm to the working tooth surface and the blending surface of variable ratio rack is designed.Based on engineering examples,the digital design of the point cloud of variable ratio rack of mechanical variable ratio steering gear is achieved in MATLAB.(2)According to the tooth surface’s characteristics of variable ratio rack,the feasibility of its processing method is analyzed.According to the two-parameter envelope theory,the mathematical model of grinding including generating motion and feed motion is deduced.According to the tooth surface equation of tools and mathematical model for machining,the grinding variable ratio rack’s coordinate system is established and it’s tooth surface equation is derived,then the correctness of this grinding method is verified theoretically.Reasonable discrete grinding parameters are set to ensure the machining of the characteristic contact line of the variable ratio rack’s tooth surface.(3)Taking the variable ratio rack of circulating ball type variable ratio steering gear as an example,a virtual machining method is designed by combining the grinding method of the variable ratio rack’s tooth surface,the virtual machining environment is configured in VERICUT,and the grinding G code is prepared,then the virtual machining of the variable ratio rack of circulating ball type variable ratio steering gear is achieved,and the feasibility of the grinding method and the effectiveness of grinding the variable ratio rack’s tooth surface are verified.The research work in this paper can improve the design efficiency and design accuracy of the variable ratio rack of mechanical variable ratio steering gear,shorten the development period and reduce the cost of research,and improve the market competitiveness.At the same time,it can provide machining method and technical guidance for the manufacture of the variable ratio rack of mechanical variable ratio steering gear,thereby promoting the application of the mechanical variable ratio steering gear.